Rotational spectra have been assigned for the 129XeH35Cl, 129XeH37Cl, 129XeD35Cl, 131XeH35Cl and 132XeH35Cl van der Waals molecules by employing pulsed microwaveFourier transform spectroscopy in a Fabry–Perot cavity with a pulsed supersonic nozzle as the molecular source. The rotational constants, centrifugal distortion constants, and Cl nuclear quadrupole coupling constants obtained from the spectra are used to determine the structure of XeHCl and to gain information on the intermolecular potential binding of Xe to HCl. From the spectrum of 131XeH35Cl and an analysis of the centrifugal distortion in 129XeH35Cl, 131XeH35Cl, and 132XeH35Cl the 131Xe nuclear quadrupole coupling constant in XeHCl is found to be −4.9±0.2 MHz. Using the known nuclear quadrupole moment of 131Xe, the electric field gradient at the Xe nucleus is calculated. The observed field gradient is discussed in terms of Sternheimer shielding and formation of the weak Xe–HCl van der Waals bond.

Vibrational optical activity arising from perturbed degenerate modes (PDM) is defined in terms of the chiral perturbation of symmetric chemical groups containing degenerate pairs of modes. This approach predicts that each such degenerate pair of vibrations will give rise to a couplet signal having equal and opposite VOA intensity for the two modes. The PDM formalism is developed explicitly for the case of a chemical group of C3v symmetry in vibrational circular dichroism (VCD), which complements earlier descriptions of degeneracy in Raman optical activity (ROA). Calculations using the fixed partial charge (FPC) model for VCD and the atom dipole interaction (ADI) model of ROA were carried out for the molecules (R)‐1‐bromo‐1‐chloro‐1‐fluoroethane and (S)‐1‐chlor‐1‐fluoroethane‐1‐d1 (and d0) as simple examples of molecules with a methyl group in a chiral environment. To further analyze the nature of the chiral perturbation of the methyl group, VOA calculations for bromochlorofluoroethane were carried out for perturbations of charge or polarizability, mass, geometry and potential energy, applied individually and in combination to the symmetric parent molecule 1,1,1‐trichloroethane. In most cases degenerate mode pairs gave calculated VOA couplets of nearly equal and opposite intensity. The signs and magnitudes of these couplets are discussed in relation to the perturbations applied. It is found that different types of degenerate vibrations behave differently thus reducing the scope of generalizations regarding the effect of the chiral perturbations. However, a more consistent picture emerges if the net sign of the combined VOA from each degenerate mode pair is used and a strong correlation of these signs to the sign of the methyl torsion mode is apparent. The significance of these results to actual VOA observation and interpretation is discussed.

Infrared absorption spectra are reported for matrix isolated (CuCl)n, (CuBr)n, (AgCl)n, (AgBr)n and for mixed clusters with composition CunClmBrn–m. Silver halide clusters with n=1 to 3 are already present in the vapor in equilibrium with the melt. The monomer and dimer forms of the copper halides could be produced only by using a two‐stage oven to partially dissociate the predominant trimer. The stable configurations and corresponding infrared active vibrational frequencies are calculated and compared with experiment. By means of this comparison we come to the following tentative conclusions concerning the structure of these clusters: The silver dimers appear to be rhombic with an X–M–X angle differing considerably from 90°. Both the Cu and the Ag halide trimers are deformed six‐rings. The Cu halide tetramer appears to be an eight‐ring, not a cube. Larger clusters, (MX)6,7,8, formed within the matrix at high halide to argon concentrations also appear to have planar structures.

The Raman line shapes and frequencies of the ν4 asymmetric (C=CH2) stretching mode at 1657 cm−1 and the ν9 symmetric (C–CH3) stretching mode at 805 cm−1 (both of symmetry A1) have been measured in dilute solutions of isobutylene in several polar and nonpolar solvents. The frequency shifts in the different solutions can be interpreted in terms of repulsion, dispersion, induction, and dipolar forces between molecular bonds. The induction and dipolar forces play only a minor role. The blue shift due to the repulsion forces and the red shift due to the attractive dispersion forces are nearly equal for ν9, while the dispersion forces are much more important for ν4. Analogous behavior has already been described in our earlier work dealing with pure compressed isobutylene. The frequency shift and the linewidth are connected via the first and second spectral moments, and the order of magnitude of the width can be predicted from the frequency shifts. However, quantitative calculations are more difficult for linewidths than for shifts. Qualitatively, the linewidth behavior is consistent with the result for the vibrational frequencies concerning the relative importance of the repulsive and attractive energies.

Fluorescence decays of a monolayer of rhodamine B on single crystals of anthracene, phenanthrene, and naphthalene have been measured for the first time with a picosecond laser and a streak camera. The fluorescence decays were not single exponentials. Two different decay characteristics have been observed corresponding to an exo‐ and endo‐energetic electron transferreaction between excited dye and substrate. The short decay of 35±7 ps on an anthracene crystal is explained by the electron‐transfer kinetics from anthracene to excited rhodamine B. In the cases of naphthalene and phenanthrene,the electron transferreaction becomes endo‐energetic and slower. The decays within several tens of picoseconds are analyzed in terms of two‐dimensional Förster‐type energy transfer to quencher sites where dyes are suggested to be in contact with each other. In connection to this phenomenon, the concentration quenching of the fluorescence of rhodamine B in aqueous solution was elucidated in terms of the Förster‐type energy transfer to the nonfluorescent dimer leading to a nonexponential decay.

The temperature dependence of the time‐resolved laser‐induced fluorescence(LIF) of gaseous UF6 has been investigated in 10 °C increments from −30 to 80 °C over the 0.005–85 Torr pressure range. The UF6 was excited to the A state with a pulsed dye laser at 392.1 nm and the fluorescence emission peaked at 421 nm and was monitored to determine the LIF lifetime. The pressure/lifetime data at each temperature have been fit by computer with our LIF kinetic expression reported previously in this journal [J. Chem. Phys. 69, 2181 (1978)]. The six quenching rate constants of our kinetic model have been evaluated in terms of their temperature dependences. Each rate constant has been represented with an Arrhenius type expression; pre‐exponential A factors and activation energies are presented.

The Rayleigh linewidth of a methane (71.07%)–ethane mixture was measured by dynamic light scattering near the plait point. Results are reported for the concentration diffusivity and (preliminary only) for the thermal diffusivity. It was found that a large background contribution is present in the concentration diffusivity, in agreement with theoretical predictions. The thermal diffusivity is compared to a one‐fluid model introduced previously. A critical temperature of 236.36±0.03 K and a critical pressure of 6.66±0.02 MPa was determined for the mixture.

In this work we report the first thermoluminescence (TL) and emission spectra studies of the sulphur‐containing DNA base analog 6‐methylmercaptopurine (6MeMP), and its riboside, 6‐methylmercaptopurine riboside (6MeMPR),x irradiated at 10 K. The 6MeMP glow curve exhibits TL peaks at 28, 40, 68, 78, 112, and 140 K with typical emission from each peak consisting of a band possessing maxima at 500 and 530 nm. Only three prominent peaks were found in the 6MeMPR glow curve: 42, 52, and 140 K. Typical emission from each of these TL peaks consisted of a band with maxima at 455 and 485 nm. Thermal activation energies and frequency factors associated with each glow peak were extracted from the experimental data and used in formulating a model to explain the observed emission. Ultraviolet (UV)‐induced glow curves, emission spectra, and photobleaching studies were also conducted in efforts to deduce the mechanisms of charge recombination in 6MeMP and 6MeMPR. The results indicate that metastable states exist in both 6MeMP and 6MeMPR which are filled by ionizing radiation. TL occurs when these trapped charges are thermally released and decay to the ground state (So) via the first excited singlet state (S1) or the first excited triplet state (T1). An energy level diagram depicting the TL emission process is presented which shows that the energy separation of S1 and T1 is approximately 0.14 eV. Further, we find that some of the TL peaks in both samples possess thermal activation energies less than 0.14 eV, suggesting that they lie between S1 and T1 in energy; these peaks are characterized by unusually small frequency factors (0.3 to 3000) s−1. Our results are consistent with a model originally proposed by Weissbluth etal. and modified by Tatake etal. to explain TL in nucleic acid bases. Finally, we suggest that the 140 K peak in 6MeMP results from the thermal destruction of an electron‐adduct radical whose molecular structure and thermal properties have been previously determined by ESR studies.

The CARS (coherent anti‐Stokes Raman scattering) line shapes of the 1362 cm−1 Raman transition of dilute aqueous FeII cytochrome c have been studied with excitation in the region of the Soret band. In contrast to previous results for flavin, for which a Lorentzian CARS peak was observed at the electronic origin, the Lorentzian peak for cytochrome c occurs on the low energy side of the absorption band. The relative positions of the dispersive and negative line shapes are also red‐shifted compared to flavin. When the scattering model previously developed for flavin is extended to include higher vibrational levels of the excited state, the cytochrome c pattern emerges as a consequence of a small origin shift parameter for the 1362 cm−1 mode. A line shape analysis for β‐carotene indicates large origin shift parameters, near unity, for the vibrational modes at 1525, 1155, and 1005 cm−1, in agreement with previous analyses of the spontaneous Raman and CARS excitation profiles. Inclusion of multimode terms in the scattering model, however, decreases the estimated origin shifts substantially.

Using the results from two‐photon excitation experiments it is shown that a low lying FC shifted state is present in La2O2S–Tm3+. The thermal quenching of the 1I6 emissions can be explained in terms of thermally promoted crossovers to this FC shifted state.

Solid state, low temperature IR (25–7400 cm−1) and Raman (100–2600 cm−1) spectra were obtained for Np(BH4)4 and Np(BD4)4 from which most of the allowed fundamentals were assigned based on the Tdmolecular structure. Those assignments were used in a normal coordinate analysis to derive a simple force field using eight primary and five interaction constants. This field is very similar to those found for Zr(BH4)4 and Hf(BH4)4. Isotopic impurity, overtone, and combination bands were identified in the IR spectra with the help of the normal coordinate calculations. Near IR spectra of Zr(BH4)4 and Zr(BD4)4 were taken in the range 7400–4000 cm−1 and the observed absorption bands were assigned as either overtone or combination levels.

The effect of intermolecular interaction on the Raman spectrum of two modes which are in Fermi resonance has been investigated theoretically. The theory includes the resonance exchange of vibrational energy as well as the inter‐ and intramolecular Fermi coupling interaction and is expected to be a realistic model for the interpretation of the concentration dependence of the observed Raman spectral features of the Fermi resonance bands of liquid NH3 and other molecular liquids. Explicit microscopic expressions for the Fermi interaction parameter, the peak positions, and linewidths of the Fermi‐resonance bands are provided. It is shown that the peak positions of the two coupled bands will be dependent on the concentration of the scattering molecules, and for the case of strong coupling the Fermi interaction parameter will have a nonlinear concentration dependence, as observed in NH3 dissolved in various solvents.

A supersonic free jet expansion has been used to produce the van der Waals complexes of I2 with ortho‐ and para‐H2 and D2. The results of fluorescence excitation and dispersed emission spectroscopy were combined to deduce the parameters of the isotropic part of the intermolecular potential. Using a Morse potential these were found to be De=122 cm−1 and ωe=106 cm−1. Observations were made which also indicate the presence of anisotropy in the potential: different absorption frequencies for complexes containing ortho and para forms of H2 and D2, and different product state distributions when ortho and para H2I2 vibrationally predissociate. Approximate measurements of vibrational predissociation lifetimes of I2H2 and some I2–rare gas complexes are reported here, and their dependence on various molecular and intermolecular potential parameters is discussed in light of current theoretical treatments, namely,the energy gap law of Beswick and Jortner and the momentum gap law of Ewing. In the case of o‐H2I2, the relatively high van der Waals stretching frequency (ωe?100 cm−1) is well‐matched to that of the I2 stretching frequency (ωe?128 cm−1 in the B3Π state), resulting in good coupling between the initial bound state (prepared by laser excitation) and the final dissociative state. Hence, a comparatively short vibrational predissociation lifetime of ∼18 psec is observed.

In this electron energy loss investigation of the electronic states of trans‐1,3‐butadiene, high energy resolution (25 meV) and a wide range of incident energies (9.5 to 49 eV) have been employed to locate and assign valence and Rydberg transitions in the typically congested 5–9 eV (2500 to 1400 Å) region of the spectrum of a polyatomic molecule. Comparisons of the observed relative differential scattering cross sections (DCS) of various features in the lower energy (5.0 to 6.8 eV) region with the unambiguous assignments of these features from optical absorption and multiphoton ionizationspectra allowed certain conclusions to be drawn regarding the typical DCS of Rydberg and valence singlet–singlet transitions. These ’’rules’’ have been applied to the congested 7–9 eV energy loss region of the butadiene spectrum. A diffuse process near 7.3 eV has been assigned as a forbidden valence transition, probably 1Ag←1Ag, on the basis of its relative DCS. The identification of the 7.07 and 8.00 eV transitions as successive members of the same Rydberg series is supported, and both transitions are demonstrated to contain considerable valence component.

The predominant free radicals trapped in single crystals of the 1:1 intermolecular complex of imidazole and 5,5‐diethylbarbituric acid (barbital) x‐irradiated at 12 K have been identified by ESR and ENDOR. The electron abstraction and electron addition products are found to be the imidazole π cation and the barbital π anion, respectively. The π cation provides experimental evidence of evenly distributed unpaired electron density at positions C2, C4, and C5 of the five membered imidazole ring. In the π anion the unpaired electron density is localized primarily on C4 of barbital. It is suggested that π anions are trapped in barbital in preference to imidazole because barbital has a higher cross section for electron capture than imidazole. On the other hand, π cations are trapped in imidazole in preference to barbital because the barbital π cation has a higher cross section for destruction than the imidazole π cation.

Liquid water was irradiated with a nanosecond pulsed electron beam and the emitted light was examined for any non‐?erenkov emission in the wavelength range 210–380 nm. In order to avoid interfacial effects associated with containment, a transient jet of liquid water was irradiated while it traversed an evacuated chamber having dimensions considerably larger than the jet. Analysis of the decay profiles and peak intensities of the emitted luminescence provided no evidence for the existence of a non‐?erenkov component in the emission.

Polarized Raman spectra were measured on single‐crystal specimens of orthorhombic n‐C35H72 and monoclinic n‐C36H74, both consisting of the orthorhombic polyethylene (o‐PE) subcells. Relative magnitudes of the squared elements of the derived polarizabilitytensor were evaluated for every zone‐center fundamentals of the o‐PE lattice. These values were proved to reproduce well the observed Raman intensities of uniaxially oriented and unoriented samples of PE. The polarizations, the frequencies, and the intensity ratios of the components of the doublets due to the crystal‐field splitting were measured for all the internal modes except for the CH2 stretching vibrations, using a single‐crystal specimen of n‐C35H72 cooled at liquid helium temperature. They agreed with the results of the normal coordinate treatment of the o‐PE lattice. The Raman activity of the B3g component of the CH2 rocking mode was found to vanish as predicted by the oriented‐gas model approximation.

Results of a fully three‐dimensional classical trajectory calculation of vibrational energy transfer are presented for the collision of HF(v=1) with HF(v=1) and its deuterium analog. A cross‐correlation method, together with quasiclassical trajectories, is introduced to relate the changes in vibrational states of the two molecules to probabilities and rate constants. Multiple collisions are found to make an important contribution to the vibrational energy transfer cross‐sections for the present potential surface. Vibrational anharmonicity is shown to decrease the energy transfer rate constant by a factor of ten, by causing the process to be further from exact resonance. Excellent agreement with experiment is obtained for the HF–HF and DF–DF systems.

We apply a rotational decoupling scheme related to the infinite order sudden approximation to treat vibrational predissociation of the triatomic van der Waals molecule HeI2. The potential surface is described by the sum of three Morse potentials between individual bonds. The total rate for vibrational predissociation as a function of vibrational excitation is compared with the results obtained for the colinear and T‐shaped models. Final rotational distributions for the I2 fragment are also obtained.

Measurement of the isotopic selectivity as a function of temperature are described for IR laser induced dissociation of UO2(hfacac)2⋅THF in a low density molecular beam. The measured selectivity was found to increase from 1.2 at 120 °C to 1.9 at 65 °C. This behavior is consistent with a model which takes into account both the initial thermal energy content of the molecule and the energy barrier to dissociation. Indeed, such behavior is expected for any complex molecule which has isotopically shifted, but overlapping absorption spectra as is the case for the 235U and 238U containing molecules used in this study.